1. Technical Field of the Invention
The present invention relates to cellular telephone systems and, in particular, to a fixed cellular communications system.
2. Description of Related Art
Most people who already have telephone service take their telephone service for granted. They do not realize that in many locations telephone service is a limited resource, and that service providers are often hard pressed to offer that service to all who desire it. Wire-based telephone service providers simply cannot keep up with the recent surge in demand for telephone service. While a large portion of this demand can be traced to the increased use of facsimile machines (which each may require a separate telephone number), an equally significant source of demand can be traced to the increased numbers of people who now want and can afford telephone service. Many times, the increases in population and accompanying increases in demand for telephone service occur in areas where the existing wire-based telephone system infrastructure is either inadequate to handle the increased demand or is completely nonexistent. In such cases, people must wait for the service provider to take the steps needed to establish the required telephone system and catch-up with the demand. Waits as long as several months for a new telephone number, and several years for the installation of wire-based telephone systems having adequate capacity, are not uncommon in heavily populated cities or remote locations.
The planning costs involved in expanding existing or initiating new wire-based telephone systems are enormous when you consider the need for both the acquisition of rights of way and the renovation or construction of the service providing infrastructure (comprising, for example, the switching networks and the laying or stringing of telephone cable). However, before making these expenditures, wire-based telephone service providers must know (or be able to accurately project) exactly where their customers will be located, how many customers will be there, and when they are going to arrive and need the service. It is often the case that service providers act in a reactionary rather than proactive manner with respect to subscriber demand, and are accordingly not prepared to meet the increases in demand in a timely fashion. This failure is caused primarily by the significant time delay experienced from the point of approving the provision of a wire-based telephone system and its actual installation and placement into operation. These delays have caused telephone service providers to re-think the use of conventional wire-based telephone systems when addressing pending needs for telephone service initiation or expansion.
Cellular telephone systems provide an attractive alternative to conventional wire-based telephone systems, especially in connection with the provision of new or expanded telephone service in heavily populated or remote areas where significant increases in demand are or have been encountered. The expense, aggravation and time involved in acquiring rights of way and establishing the infrastructure to provide telephone service are obviated or substantially reduced with the installation and use of a cellular telephone system. However, the cost to the subscriber on a monthly or per call basis often drastically exceeds the cost for similar activities incurred with respect to wire-based telephone systems. Furthermore, the mobility advantage of cellular telephone systems, which is accounted for in the increased subscriber cost of the service, is often a feature that many telephone service users do not want to pay for or necessarily need.
Accordingly, efforts have been made to couple cellular systems with conventional analog telephones and provide a hybrid telephone system wherein telephone sets are fixed at certain locations as in a wire-based system but instead access the telephone network using radio frequency communications in a cellular environment. Such systems, conventionally referred to as fixed cellular systems, interface a conventional analog telephone set, like that used in wire-based telephone systems, with a radio frequency transceiver, like that used in a mobile telephone, operating within a cellular telephone system. The primary advantages of fixed cellular systems are the elimination of the costs and hassles of acquiring rights of way and laying or stringing telephone cables, and the ease and swiftness with which the system may be installed and made operational. The availability of a fixed cellular system thus offers service providers a tool for quickly reacting to increases in demand at a reasonable provider and subscriber expense.
In spite of the fact that the subscriber's communication device (telephone set) looks like a conventional analog wire-based telephone set, the telephone set in a fixed cellular system unfortunately operates like a cellular mobile telephone, and thus suffers from the known caller interface disadvantages and inconveniences experienced with cellular service. For example, when a call is to be initiated in a fixed cellular system, the phone number must be first completely dialed into in the telephone set through the keypad and then sent to the cellular system for processing. No instantaneous feedback is provided to the caller during the dialing operation concerning the propriety of the entered numbers. The transmission of the dialed number over the cellular network is made only after the activation by the caller of a send button on the keypad. The caller must then wait while the cellular network side of the system selects the voice channel to carry the conversation and completes the call to the called party. The fixed cellular system caller interface accordingly and undesirably operates more slowly relative to, and in a manner completely foreign to the manner of operation experienced in, a conventional wire-based telephone system.
Efforts have been made to have the fixed cellular system mimic operation of the wire-based telephone system with respect to some aspects of the caller interface. For example, it is known to include functionality for simulating at the cellular system interface the dial tone and reorder tones heard on conventional wire-based systems before and during the caller dialing operation. Also, functionality has been provided in fixed cellular systems for automatically generating the send command at the cellular system interface following completion of caller entry of a telephone number. With these features, the analog telephone set connected to a fixed cellular system operates more like a conventional wire-based telephone set than a cellular mobile station. However, this caller interface is slow and does not function to monitor the propriety of the caller dialed numbers during the dialing operation.
Another proposed solution addressing these problems responds to an off-hook condition of the analog telephone set by establishing a cellular traffic channel connection to the cellular network, and applying a dial tone to that traffic channel connection. The applied dial tone prompts the user to enter digits which are then transmitted as dual tone multi-frequency (DTMF) tones over the traffic channel connection for network evaluation and processing. Use of the traffic channel connection is this manner has proven, however, to be a rather unreliable transport mechanism for the dialed digits. The audio path supporting the traffic channel connection further supports the fast associated control channel (FACCH) which is used for carrying certain call related cellular network control communications. When these communications are sent to the network, the audio path must be muted. If the muting occurs at or about the same time that a DTMF tone is being sent to the network over the traffic channel, the sent tone may be mangled or lost, and thus may not be detected by the network. Failure of the call set-up then results. A solution to this problem is needed.